The seven-time Grand Slam title winner announced on Twitter and her website that she wouldn't play in the year's first major tournament, which starts next week. She added, though, that she plans to be back in action next month.Williams hasn't played competitively since August 29 at the US Open. Two days later, she pulled out of that tournament, revealing that she'd been diagnosed with Sjogren's syndrome."I regret to announce that I am withdrawing from the 2012 Australian Open. After several months of training and treatment, I am making steady progress to top competitive form. My diet and fitness regimen have allowed me to make great strides in terms of my health and I am very close to being ready to return to WTA competition," Williams said in a posting on her website Monday. "I have every intention to return to the circuit in February."The 31-year-old American is a former No. 1 who is 100th in this week's WTA rankings. She's dealt with a series of health problems, including a hip injury that forced her to withdraw from last year's Australian Open, and a left knee injury that kept her on the sideline between Wimbledon and the U.S. Open in 2010.Since reaching the semifinals at the 2010 US Open, Williams has played only 11 matches.After winning her opener at Flushing Meadows in August  which was Williams' first match in two months  she withdrew shortly before her second-round match there.At that time, she described the way she'd been feeling this way: "It was just energy-sucking, and I just couldn't play pro tennis."Her younger sister Serena, whose 13 Grand Slam titles include five at the Australian Open, badly sprained her left ankle at a tournament in Brisbane this month. It's not clear whether Serena will be able to play at the Australian Open.